1. Field
The present disclosure relates generally to processing data and in particular to processing data from responses of a structure to an input waveform. Still more particularly, the present disclosure relates to a method, apparatus, and computer usable program code for identifying modes within a response signal received from a structure.
2. Background
Composite and metallic aircraft structures may be susceptible to internal changes that may occur from fatigue, impacts, and other events or conditions. Composite materials typically have a minimal visual indication of these types of changes. As a result, an aircraft may be inspected to assess the integrity of the structure on a periodic basis or after visual indications of surface anomalies, such as dents and scratches.
For example, impacts to a structure, such as an aircraft, may occur during cargo loading and unloading. These types of impacts may warrant an inspection to determine whether changes or anomalies have occurred as a result of these impacts. Inspection of the structure of an aircraft may be time-consuming and costly in terms of the time and skill needed to perform the inspection. Further, an airline may incur lost revenues due to the aircraft being out of service.
Structural health monitoring techniques have been developed and used to monitor materials and structures. These techniques often build the health monitoring systems into the structures. These health monitoring systems may be used to determine whether changes have occurred to these materials and structures over time.
Sudden changes in environment, such as electromagnetic effects, mechanical stresses, and other environmental effects may affect the integrity of various materials and structures over time. By having health monitoring systems built into or associated with the structures to monitor the structures during use, appropriate measures and responses may be taken to prevent catastrophic failures and may prolong the lifespan of these structures.
The monitoring of structures may include various non-destructive elevation methods, such as ultrasonic testing or x-ray testing. Ultrasonic testing uses contact-based transducers to mechanically scan a structure. These distributed sensors and actuators may be surface mounted on the structure or may be embedded in the structure to generate and propagate diagnostic signals into the structure being monitored.
A structural health monitoring system is based on using a transmitter and sensor configuration to transmit waveforms at various frequency ranges and to acquire data from the responses. Oftentimes, a transducer may function both as a transmitter and a sensor. Structural health monitoring systems may be employed in structures as onboard or integrated systems for detecting and characterizing anomalies or changes that may require maintenance.
Currently used structural health monitoring systems may require data from a large number of sensors attached to or embedded within the structure. The number of sensors may be large in order to obtain the data needed to identify the location for an anomaly. Currently used structural health monitoring systems may perform triangulation in which coordinates or estimates of a location of an anomaly may be calculated from data obtained from a number of different sensors.
It would be desirable to reduce the number of sensors needed to obtain an estimate of a location of an anomaly within a structure. The reduction in the number of sensors may reduce weight and complexity for a structural health monitoring system.
Therefore, it would be advantageous to have a method and apparatus that overcomes one or more of the problems described above.